MDS 1st Year Prosthodontics

Theory Questions - 10 Marks Each

(MUHS Pattern | All Subjects)

COMPLETE DENTURE PROSTHODONTICS

• Definition of neutral zone (zone of minimal conflict between tongue and cheek/lip musculature)
• Anatomical basis and musculature involved (buccinator, orbicularis oris, tongue)
• Indications (resorbed ridges, hyperactive tongue, previous denture failure)
• Technique steps:
  • Fabrication of special trays
  • Recording with impression compound/polyvinyl siloxane
  • Wax addition and tooth positioning within the neutral zone
• Advantages over conventional tooth positioning
• Clinical significance: improved stability, reduced ridge resorption, patient comfort
• Limitations and contraindications
• Recent modifications (Beresin-Schiesser technique)

• Classification (elastic: reversible/irreversible, non-elastic: rigid/thermoplastic)
• Addition silicone (polyvinyl siloxane / PVS):
  • Chemistry and setting reaction (hydrosilylation)
  • Types: monophase, light/heavy/medium body
  • Properties: dimensional stability, accuracy, hydrophilicity (surfactant-modified), tear resistance
  • Manipulation: mixing ratio, working and setting time, temperature effects
  • Clinical applications in CD: final impressions, border moulding, single-step/double-mix technique
  • Advantages over ZOE and polysulfide
  • Storage and disinfection
• Recent advances: hydrophilic PVS, automix cartridges

FIXED PARTIAL DENTURES / CROWN & BRIDGE

• Definition and indications for metal-ceramic crowns (PFM)
• Classification of tooth preparations (shoulder, chamfer, knife-edge, beveled shoulder)
• Step-by-step preparation for maxillary central incisor:
  • Incisal reduction: 1.5-2 mm
  • Labial reduction: 1.2-1.5 mm (two-plane)
  • Lingual reduction: 0.5-1 mm (metal collar or porcelain lingual)
  • Proximal reduction and path of insertion
  • Finish line: shoulder with bevel (labial), chamfer (lingual)
• Biological width consideration and crown lengthening
• Ferrule effect (not applicable but margin placement)
• Aesthetic zone principles: translucency, margin at/below gingival level
• Common errors and their clinical consequences
• Metal-free alternatives and why PFM is still relevant

• Biomechanics: lever arm, fulcrum, stress distribution
• Ante's Law: PDL area of abutments >= PDL area of pontic teeth
• Abutment evaluation factors:
  • Crown-root ratio (ideal 2:3, minimum 1:1)
  • Root form and number (multi-rooted preferred)
  • Bone support (alveolar bone level, angular defects)
  • Mobility (Miller's classification, acceptable mobility)
  • Pulpal status (endodontically treated teeth as abutments)
  • Strategic value
  • Periodontal health
• Span length and pontic design consideration
• Role of pier abutment and stress breakers
• Cantilever vs. fixed-fixed design
• Clinical decision-making algorithm

REMOVABLE PARTIAL DENTURES

• Kennedy's classification with Applegate's rules
• Kennedy Class I: bilateral free-end saddle (unique challenges)
• RPD components and their specific roles in Class I:
  • Major connector: lingual bar / lingual plate (indications)
  • Minor connectors
  • Rests: occlusal, cingulum, incisal - position and function
  • Clasps: RPI clasp (Krol's system), RPA clasp - rationale for free-end saddle
  • Indirect retainers: importance in Class I to prevent rotation
• Biomechanical challenges: rotation around rest seats, functional movement
• Implant-assisted RPD consideration
• Relining and follow-up protocol
• Differentiating Class I from implant-retained overdenture

• Definition and historical evolution (Chayes, 1906)
• Classification:
  • By location: intracoronal, extracoronal, bar type, stud type
  • By stress transfer: rigid, resilient, semi-precision
  • By mechanism: friction-retained, locking, ball-socket
• Intracoronal attachments:
  • Examples: Stern G/A, Crismani, micro-attachments
  • Preparation requirements (minimal tooth structure)
  • Stress distribution (direct load transfer)
  • Aesthetics (no visible clasps)
• Advantages: aesthetics, improved retention, patient acceptance
• Limitations: cost, tooth preparation, maintenance, laboratory complexity
• Indications and contraindications
• Wear and replacement protocols
• Comparison with extracoronal attachments

DENTAL MATERIALS

• Classification: feldspathic, leucite-reinforced, lithium disilicate, zirconia, alumina, hybrid
• Zirconia (Y-TZP - Yttria-stabilized Tetragonal Zirconia Polycrystal):
  • Composition: ZrO2 + 3 mol% Y2O3
  • Crystal structure: monoclinic, tetragonal, cubic phases
  • Transformation toughening mechanism
  • Properties: flexural strength (900-1200 MPa), fracture toughness, opacity (traditional) vs. translucency (multilayer, 5Y-TZP)
  • Processing: CAD/CAM, pre-sintered vs. fully sintered milling
  • Surface treatment: air abrasion, acid etching limitations, bonding protocols (MDP primer, Zirconia primer)
• Clinical applications: posterior crowns, FPD frameworks, implant abutments, full-arch restorations
• Aging/low-temperature degradation (LTD)
• Recent advances: translucent multilayer zirconia, cubic zirconia

• Elastomeric impression materials overview
• Condensation Silicone (polydimethylsiloxane):
  • Chemistry: condensation polymerization, tin catalyst, ethanol byproduct
  • Properties: dimensional change (0.6-1.0%), working/setting time
  • Hydrophobicity, tear resistance
  • Limitations: byproduct release, poor long-term stability
• Addition Silicone (PVS):
  • Chemistry: hydrosilylation, platinum catalyst, no byproduct
  • Properties: dimensional change (<0.05%), superior accuracy
  • Hydrophilicity (surfactant-modified), detail reproduction
  • Handling: inhibition by sulfur compounds, latex, eugenol
• Comparative table: dimensional stability, accuracy, cost, shelf life, hydrophilicity, disinfection compatibility
• Clinical selection criteria
• Automix vs. hand-mix systems
• Pouring time and stone compatibility

IMPLANTOLOGY / IMPLANT PROSTHODONTICS

• Definition (Branemark 1969, 1985): direct structural and functional connection between living bone and implant surface
• Biological basis:
  • Primary stability (mechanical) vs. secondary stability (biological)
  • Healing sequence: blood clot, woven bone, lamellar bone, bone remodeling
  • Peri-implant bone remodeling (Wolff's law)
• Factors affecting osseointegration:
  • Implant factors: material (titanium, PEEK, zirconia), surface texture, design (thread pitch)
  • Host factors: bone quality (Lekholm-Zarb), quantity, vascularity, systemic conditions
  • Surgical factors: heat generation, irrigation, primary stability (ISQ value)
  • Loading factors: timing (immediate, early, conventional)
• Clinical assessment: ISQ (Osstell resonance frequency analysis), percussion test, mobility, periapical radiograph, CBCT
• Surface modifications:
  • Subtraction: acid etching (SLA surface), sandblasting (SLActive)
  • Addition: TiO2 coating, hydroxyapatite coating, fluoride surface, laser surface texturing
  • Biochemical: RGD peptides, growth factor incorporation
• Evidence for improved BIC (bone-implant contact) with modified surfaces

OCCLUSION / GNATHOLOGY

• Definition evolution: Gysi (1910) to current GPT-9 definition - "most superior, anterior position of condyles in the articular fossa"
• Importance: reproducible, not dependent on teeth, physiological reference point
• Centric Relation vs. Centric Occlusion:
  • CO = maximum intercuspation (tooth-determined)
  • CR = condylar (joint-determined)
  • CR-CO discrepancy: significance, long centric concept
• Methods of recording CR:
  • Bimanual manipulation technique (Dawson)
  • Chin point guidance (Gysi)
  • Leaf gauge technique
  • Anterior deprogrammer (Lucia jig)
  • Gothic arch tracing (intraoral/extraoral)
  • Bilateral manipulation (Dawson modification)
• Recording media: wax, ZOE paste, acrylic resin, polyvinyl siloxane bite registration material
• Verification methods: check bites, articulator mounting
• Clinical significance: complete dentures, occlusal rehabilitation, TMD treatment, implant prosthetics
• Long centric and freedom in centric concept

Marking Scheme (10 Marks Each)

Tips for MUHS MDS 1st Year Exams

1. Diagrams carry marks - always include labeled diagrams (cross-section of implant surface, RPD design, impression material setting reactions)
2. Recent advances - always add a brief paragraph on latest evidence or technology
3. Clinical significance - relate all answers back to clinical practice
4. Flowcharts and tables - use comparison tables (e.g., addition vs. condensation silicone) to present information clearly
5. References - mentioning landmark studies (Branemark for osseointegration, Krol for RPI clasp) impresses examiners